President Obama and Russian President Dmitry Medvedev signed the Strategic Arms Reduction Treaty in 2010 that imposed, over time, a limit on the number of deployed warheads the United States and Russia could have at 1,500. Relations between the United States and Russia have soured over the past several months over issues ranging from the crisis in Syria to human rights in Russia. Obama and Medvedev's successor, Vladimir Putin, are scheduled to hold a summit in September.

Developments

April 15: Russian officials say White House national security adviser Tom Donilon hand-delivered a letter to Putin from Obama in a bid to improve relations.